The present invention relates to a positive photoresist composition sensitive to a far ultraviolet ray for use in fine fabrication, for example, semiconductor devices. More specifically, the present invention relates to a positive photoresist composition suitable for far ultraviolet ray exposure.
The degree of integration of integrated circuits has recently become much higher, and the processing of ultrafine patterns having a line width of a half micron or below is required in the production of semiconductor substrate for VSLI. In order to meet such a requirement, a wavelength of light source used in an exposure apparatus for photolithography becomes shorter, and nowadays the use of an excimer laser beam (e.g., XeCl, KrF or ArF) in a short wavelength region of a far ultraviolet ray is investigated.
As a resist for use in the pattern formation by the photolithography in such a wavelength region, a chemically amplified resist is known.
In general, the chemically amplified resist is roughly divided into three types, i.e., the so-called two-component, two point five-component and three-component types. The chemically amplified resist of two-component type comprises a combination of a compound (hereinafter referred to as a xe2x80x9cphoto-acid generatorxe2x80x9d sometimes) capable of generating an acid by photolysis with a binder resin. The binder resin combined with the photo-acid generator is a resin having in its molecule, a group (hereinafter referred to as an xe2x80x9cacid-decomposable groupxe2x80x9d sometimes) capable of being decomposed by the action of an acid to increase the solubility of resin in an alkali developing solution. The resist of two point five-component type further contains a low molecular weight compound having an acid-decomposable group in addition to the above described two components. The resist of three-component type contains a photo-acid generator, an alkali-soluble resin and the low molecular weight compound described above.
Although the chemically amplified resist described above is a photoresist suitable for exposure to an ultraviolet ray or a far ultraviolet ray, it is still necessary for the resist to meet requirements for characteristics from the standpoint of practical use.
As a photoresist composition for an ArF light source, a resin into which an alicyclic hydrocarbon moiety is incorporated is proposed for the purpose of improving dry etching resistance. However, the introduction of alicyclic hydrocarbon moiety is accompanied with a problem in that a system including the resin becomes extremely hydrophobic, and it is difficult to perform development with an aqueous solution of tetramethylammonium hydroxide (hereinafter referred to as TMAH sometimes), which has hitherto been widely employed as a developer for resist. Also, a phenomenon of releasing the resist film from a substrate during the development is observed.
Therefore, various investigations on introduction of hydrophilic group into the resin having alicyclic hydrocarbon moiety have been made.
Resist materials using an acid-sensitive compound containing an alkali-soluble group protected by a structure including an alicyclic group and a structure unit having a function of releasing the alkali-soluble group by an acid are described in JP-A-9-73173, JP-A-9-90637 and JP-A-10-161313 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d).
It is described in JP-A-11-109632 that a resin containing an alicyclic functional group having a polar group and an acid-decomposable group is used in a radiation-sensitive material.
A photoresist composition containing a polymer obtained by copolymerization of a (meth)acrylate derivative having a lactone structure with another polymerizable compound is described in Japanese Patent 3,042,618.
Improvements in resolution, sensitivity and dry etching resistance and low cost are attempted by using a resin containing a repeating unit wherein an alkali-soluble group is protected by a protective group including an alicyclic hydrocarbon group, a repeating unit wherein an alkali-soluble group is protected by a protective group other than the protective group including an alicyclic hydrocarbon group and a monomer unit having a lactone structure of from 10 to 35% by mole as described in JP-A-11-119434.
However, in any positive resist compositions hitherto known, problems including pattern collapsing due to insufficient adhesion and film strength, surface roughness after etching and pitch dependency, which occur accompanied with the desired miniaturization tendency of pattern, are not satisfactorily resolved.
Therefore, an object of the present invention is to provide a positive photosensitive composition in which the pattern collapsing, surface roughness after etching and pitch dependency are remarkably improved and which is preferably used in an ultramicrolithography process, for example, the production of VLSI and high capacity microtips, and in other photofabrication processes.
Other objects of the present invention will become apparent from the following description.
As a result of the intensive investigations on materials for chemically amplified positive resist compositions, it has been found that the objects of the present invention are accomplished by the positive resist compositions described below to complete the present invention.
1. A positive resist composition comprising (A) a resin, which increases a solubility rate in an alkali developing solution by the action of an acid, containing a repeating unit represented by formula (I) shown below, a repeating unit represented by formula (II) shown below and a repeating unit represented by formula (III) shown below, and (B) a compound that generates an acid upon irradiation of an actinic ray or radiation. 
In formula (I), R represents a hydrogen atom or a methyl group; A represents a single bond or a connecting group; and ALG represents any one of the groups represented by the following formulae (pI) to (pV): 
In the above formulae, R11 represents a methyl group, an ethyl group, an n-propyl group, an isobutyl group or a sec-butyl group; Z represents an atomic group necessary for forming an alicyclic hydrocarbon group together with the carbon atom; R12 to R16 each independently represent a straight chain or branched alkyl group having from 1 to 4 carbon atoms or an alicyclic hydrocarbon group, provided that at least one of R12 to R14, and either R15 or R16 represents an alicyclic hydrocarbon group; R17 to R21 each independently represent a hydrogen atom, a straight chain or branched alkyl group having from 1 to 4 carbon atoms or an alicyclic hydrocarbon group, provided that at least one of R17 to R21 represents an alicyclic hydrocarbon group, and either R19 or R21 represents a straight chain or branched alkyl group having from 1 to 4 carbon atoms or an alicyclic hydrocarbon group; and R22 to R25 each independently represent a straight chain or branched alkyl group having from 1 to 4 carbon atoms or an alicyclic hydrocarbon group, provided that at least one of R22 to R25 represents an alicyclic hydrocarbon group, or R23 and R24 may be combined with each other to form a ring; 
In formula (II) R represents a hydrogen atom or a methyl group; A represents a single bond or a connecting group; and BLG represents a chain tertiary alkyl group; 
In formula (III) R30 represent a hydrogen atom or a methyl group; R31 to R33 each independently represent a hydrogen atom, a hydroxy group or an alkyl group, provided that at least one of R31 to R33 represents a hydroxy group.
(2) The positive resist composition as described in item (1) above, wherein the resin of component (A) further contains a repeating unit including cyclohexane lactone, norbornane lactone or adamantane lactone.
(3) The positive resist composition as described in item (1) or (2) above, wherein two of R31 to R33 in the repeating unit represented by formula (III) each represent a hydroxy group.
(4) The positive resist composition as described in any one of items (1) to (3) above, wherein A and ALG in formula (I) represent a single bond and a group represented by a formula shown below, respectively. 
wherein R26 to R27 each independently represent a straight chain or branched alkyl group having from 1 to 4 carbon atoms.